1. Field of the Invention
The present invention relates to thermoplastic molding compounds with improved mechanical properties based on modified polyphenylene ethers.
2. Discussion of the Background
Polyphenylene ethers (PPE) are technical high-performance thermoplastics with high melt viscosities and softening points. They are used especially when resistance to high temperatures is important (see, e.g., U.S. Pat. Nos. 3,306,874, 3,306,875, 3,257,357, and 3,257,358). Of course, shaped parts made of pure polyphenylene ethers are brittle because of their poor impact strength, and their solvent resistance is unsatisfactory. Therefore, blends of polyphenylene ethers with other thermoplastics are ordinarily used.
DE-OS 35 18 277, for example, describes thermoplastic molding compounds based on polyphenylene ethers and polyoctenylene that are distinguished by high impact strength, outstanding high-temperature dimensional stability, and good processibility.
In contrast to these and similar alloys with an amorphous matrix, blends with polyamides have very good solvent resistance. However, as a rule, of course, brittle products are obtained, since the two components are incompatible (DE-OS 16 94 290 and 30 27 104). It is attempted in EP-OS 0 024 120 to achieve some compatibility by adding a third component such as a liquid diene polymer, an epoxide, or a compound with a double or triple bond and a functional group. However, the toughness of the resin compounds obtained is not sufficient for many applications. Better compatibility of the two phases is obtained by functionalizing the polyphenylene ether, for example with maleic anhydride, optionally together with other substances with synergistic action (for example, see EP-OS 0 232 363, DE-OS 36 15 393, DE-OS 36 21 805, and Japanese Patent Application Kokai 66,452/984). Because of the volatility and toxicity of maleic anhydride, extensive protective equipment is necessary in this case to exclude endangering the personnel or exposing them to a great extent.
Another starting point for introducing compatibility between polyphenylene ethers and other polymers consists of incorporating reactive sites in the polyphenylene ether even in the stage of oxidative coupling by adding suitable functionalized comonomers, which can react with other polymers when blended with it.
For example, a substituted aminomethylphenol is incorporated during the preparation of polyphenylene ethers in U.S. Pat. No. 4,129,555. The incorporated aminomethyl groups are intended to have the effect that blends of this polyphenylene ether with polystyrene resins will possess better impact strength.
It is shown in EP-OS 0 338 209 that a polyphenylene ether with terminal functional groups such as oxazolinyl, amide, ester, imide, or carbonyl have good compatibility with polyamides. The reaction of the functional groups with polyamide end groups can be assumed to be the reason for this.
However, it is a drawback of these previously known polyphenylene ether copolymers that they are effective only in combination with a limited number of blend components. Furthermore, the necessary comonomers are sometimes very difficult to obtain.
Although the preparation of modified polyphenylene ethers by copolycondensation, for example of 2,6-dimethylphenol with 2-methyl-6-alkylphenols, is disclosed in U.S. Pat. Nos. 3,306,874 and 3,306,875 and DE-OS 29 17 819, there is no indication to one skilled in the art either from these references or from the state of the art that the molding compounds prepared from them might have any advantages over the previously known molding compounds based on ordinary polyphenylene ethers.
Thus, there remains a need for thermoplastic molding compounds based on modified polyphenylene ethers which possess improved mechanical properties.